1. Field of the Invention
The present invention relates to a semiconductor device such as a light emitting diode, for example, to a semiconductor device housing a high-output power light emitting element which is capable of being used in domestic lighting appliances or lighting for vehicles and has excellent heat resistivity. Particularly, the present invention relates to a semiconductor device to which a reflow mounting process can be performed reliably and safely and which has high reliability even in a high temperature usage environment.
2. Description of the Related Art
A semiconductor light emitting element such as a light emitting diode and a laser diode can be used as a light source of a light emitting device. Further, in recent years, light emitting devices capable of emitting mixed white light by employing a combination of a semiconductor light emitting element and a fluorescent material which absorbs light from the semiconductor light emitting element and emits light have been in practical use for display such as indicator in electric appliances and backlight for liquid crystal displays. In addition, such light emitting devices are expected to be widely used for such as indoor lightings and in-vehicle lightings due to their higher light emitting efficiency and higher luminance.
A typically known semiconductor device includes a semiconductor element which is mounted in a package and is covered with a light translucent coating member such as epoxy resin and silicone resin. The coating member is formed in various shapes such as a lens shape in view of optical property of the semiconductor device.
The semiconductor light emitting elements in such semiconductor devices generate heat when emitting light, and abrupt change in temperature of the entire device causes expansion or contraction of the covering member which is made of a resin. This may adversely affect the light emitting elements and the bonding wires covered with the resin.
Accordingly, there has been proposed a semiconductor device in which a semiconductor element mounted on a support substrate and a thin metal wire connected to the semiconductor element are hermitically sealed with a hollow covering member (for example, see JP 2003-282953A). A semiconductor device described in JP 2003-282953A includes a support substrate mounting a semiconductor element thereon and a sealing member protecting the semiconductor element from external environment, and a hollow portion is defined by the support substrate and the sealing member so as to house the semiconductor element. With such an arrangement, the sealing member does not make contact with the light emitting element or the bonding wires. Therefore, even when the sealing member contracts by abrupt changes in temperature, the resulting stress will not be exerted on the light emitting element or the like.
However, if the hollow portion is hermetically closed by the covering member, the inner pressure of the hollow portion increases due to expansion of the gas enclosed in the hollow portion at the time of mounting the light emitting device by reflow process. As a result, stress is applied to the portion where the sealing member is bonded to the support substrate, which may result in detachment of the sealing member from the support substrate or reduction in the bonding strength, so that a semiconductor device of high reliability cannot be obtained.
Accordingly, there has been proposed a semiconductor device provided with an air vent at a portion leading from the hollow portion to the outside to reduce the gas pressure so that reflow process can be performed stably and reliably (for example, see JP2004-327955A).
However, provision of a hole in the lens body, which is a covering member, has problems such as causing lower mechanical strength and deformation of the covering member. Similar problems may occur if a hole is defined in the reflector. Also, there is a problem if a cutting work is applied to the support substrate, the air vent may be clogged by the bonding member moving thereinto. In addition, there is a problem in defining a hole or cutting processing that, due to the accuracy in such processing, the defined air vent may be somewhat too large to allow foreign matters such as dirt or dust to get in easily while serving as an air vent.
The present invention is devised to solve the aforementioned problems, and an object of the present invention is to provide a semiconductor device provided with an air vent in which reduction in the mechanical strength and deformation of the covering member is prevented and the bonding member is prevented from getting into an unnecessary portion, and an air vent of suitable size can be defined with good productivity and with good accuracy.